Hydroformylation of 1 -aryl- 1 -(2-pyridyl) ethenes catalyzed by rhodium complexes

The hydroformylation of 1-aryl-1-(2-pyridyl)ethenes 1 can be accomplished in good yield (85%) using HRh(CO) (PPh₃)₃ with rather high catalyst to substrate molar ratios (1/80) under standard conditions. Other cobalt, platinum and rhodium complexes exhibit lower catalytic activity towards hydroformylation, the hydrogenation of the substrate being in most cases the main reaction. The formation of the more branched aldehyde 3 occurs in the presence of HRh(CO) (PPh₃)₃ regiospecifically. The formation of the complex 9 from [Rh(CO)₂Cl]₂ and olefin 1a, in which only the pyridine nitrogen is coordinated to the metal, enlightens on the role played by the heteroatom in determining both chemo- and regioselectivity of the reaction.